Short-circuiting contactor for direct-current circuits



LOAD

L. H. HARRISON Filed Feb. 26, 1948 SHORT-CIRCUITING CONTACTOR FOR DIRECT-CURRENT CIRCUITS May 6, 1952 l/IQE LOAD INVENTOR L A WRENCE hf flame/sou BY 9? v% ORNEY NEGATIVE 5HU/VT o2 ill'l till. V

Patented May 6, 1952 SHORT-CIRCUITING CONTACTOR FOR DIRECT-CURRENT CIRCUITS Lawrence H. Harrison, Birmingham, Ala., as-

signor to; the United States of America as re rresentcdhy the Secretary of the Interior Application February 2d, 1948, Serial No. 11,234

2 Claims. (01. 1175-494) (Granted under the act of March 3, 1883, as amended April 30', 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government of the United States for governmental purposes without the payment to me of any royalty thereon in accordance with the provisions of the act of April 30,1928, (ch. 460.45 Stat. L. 467).

This inventionrelates to a short circuitingcontactor for direct current circuits.

In certain portions of some electricaldi'stribution systems, particularly in coal mines, it 'is essential that electrical arcs be prevented to-the greatest degree possible. When a short circuit occurs on a trailing cable carrying direct current, forces are setup tending to'separate the conductors. This results in an are being drawn which in many cases limits the currentto a value below the rating of the fuse which is intended to protect the cable from such damaging arcs. A, condition is thus set up whereby a disastrous mine fireor explosion can originate.

It is an object of this invention to provide a means of reducing the voltage on a fault by short circuiting the voltage at a preselected location.

' It is also an object of this invention to provide a. contactor device particularly adapted to short circuit a fault'on a direct current circuit.

Other objects will become apparent to those skilledin the art from the following specification taken in connection with the accompanying drawing in which:

Fig. 1 is a sectional elevation view of a short circuiting contactor constructed in accordance with the principles of this invention.

Fig. 2 is a schematic drawing showing one circuit arrangement in which the contactor of Fig. 1 may be used.

Fig. 3 is a schematic drawing showing a circuit arrangement in which the contactor device is operated by the fault current flowing through the frame of a utilizing machine.

In Fig. 1 there is provided a tube In preferably made of fiber or other insulating material. End pieces I I and I2 are each fixed to an end of tube ID, as by a threaded connection between the ends of tube I and flanges I3 and I4 of the end pieces I I and I2, respectively.

Within the tube I 9 and concentric therewith are two axially aligned magnetic core members I and I6. Through the greater part of their length core members I5 and I5 have a diameter slightly less than the internal diameter of tube It. Core member I6 at its outer end, remote from core member I5, carries a shaft 20 of reduced diameter, providing a shoulder 22 which rests against the inner surface of end member I2.

Core member I5 carries at its upper end; the end remote from core member I6, a flange I9 and a shaft 2|. I Flange I9 abuts against the up-standing flange 29 of a non-conducting annular member 32 attached to the upper surface of end member i I by the screws constituting terminals 28 and 3 I.

At their opposed adjacent ends, cores I5 and I6 carry end contact members I! and I 8 ,respec'- tively. End members I1 and I8 have a diameter greater than the adjacent portions of cores I5 and IE but less than the internal diameter of tube It so that cores I5 and I6 will freely slide therein. Core members I5 and IG'are 0f such-a length that with flange I9" and shoulder 22 in their seated positions contact members I1 and I8 are separated by a short distance.

A flat strip winding 25 is wound helically, tightly around the tube It. One end of winding 251s threaded and passes through end piece II and annular member 32 to form terminal 28. Terminal 28 is held in position by nuts abutting against endpiece II and annular member 32; The line conductor is also fastened to terminal 23 by a nut. The other end of winding 25 is also threaded and passes through end piece I2 to form terminal 30. Conductor 41] connectsterminal 30 with screw terminal 3| in end' piece I I. Terminal 30 is held in place and conductor 40 and the load conductor are fastened to terminal 39 by nuts threaded to terminal 30.

The threaded ends of winding 25 are preferably round in section. The winding 25 may advantageously be cast in helical form and slipped over the tube I0. A flexible conductor 33 connects terminal 3I with shaft 2| of core member I5; Conductor 33 has a lug at either end, one'being held under terminal screw 3I and the other being held between nuts on the threaded end of shaft 21. A negative shunt-conductor is connected to a lug held between nuts. onthe threadedend-of shaft 20.

When the contactor device of Fig. 1 i's'insta-lled in operating condition it is mountedverticall'y as shown in Fig. 1. In this condition gravity causes flange I9 of core I5 to normally seat against the member 29, and also causes the seating of shoulder 22 against the upper surface of end member I2. This maintains the ends 11 and I8 of cores l and Iii-at the proper spacing. It will be understood, however, that springs could be used to bias cores l5 and I6 into normal seating position and then allow installation in any position. The enlarged diameter of end pieces I! and 18 mini-- mizes transverse motion of the cores i5 and I6 and provides an enlarged area for electrical contact.

One method of connecting the contactor device of Fig. 1 in a distribution circuit is shown in Fig. 2 in which the contactor device 34 is shown with terminals 28 and 30 connected in series between a source of D. C. potential 35 and a load which may be a piece of utilizing machinery such as an electrical motor 39. A safety device 36, such as a fuse or circuit breaker, is shown connected in series with the contactor 34. The negative shunt conductor from core 16 is shown in Fig. 2 con nected to the negative side of the power source 35.

When a current of sufficient magnitude passes between the line and load conductors and hence through Winding 25, connected in a series therewith, core I6 is attracted to core [5 by the magnetic force produced in winding 25 until end 18 of core 16 contacts the end I! of core 15. When end pieces I! and I8 make contact, current flows between the load wire and the negative shunt wire. Since core [5 is free to move against gravity in an upward direction, cores i5 and I6, held together by magnetic attraction, may travel slightly upward together because of the momentum of the core Hi.

When cores I5 and is make contact, the positive side-of the load is connected through the negative shunt to the negative source of power source 35. This immediately eliminates the potential on the load side of the contactor and on the fault and'causes a very high current to flow from the positive side of the power source through the safety device 36, cores l5 and Hi, the negative shunt and back to the negative side of the power source 35. This will cause safety device 38 to positively and quickly operate to open the circuit.

Although the utilizing device in Fig. 2 may of necessity be placed in a position where arcing cannot be tolerated, such as against the working face of a coal mine, the short circuiting contactor 34 may be placed in a position where arcing is of little consequence, such as at the entry of the mine. Moreover, since the device 34 operates to close a circuit rather than open one, its operation. will be attended by relatively little arcing. Since core members and 16 are both free to move and since when operating there will be a large magnetic attractive force between them, they will not tend to open as by a recoil action after they have once closed.

Another method of using the contactor device of Fig. 1 is shown in Fig. 3. In this arrangement terminals 28 and 3!), and hence winding are connected in series between the frame of the utilizing device M) and the negative side of power source 35. The core is in this case is connected to the positive side of the power source 35. A switch 31 is provided between power source 35 and utilizing device A safety device 38 is connected in series with the power conductors.

When there is a fault in machine 40 and the positive wire touches the frame, a current will flow through the winding 25 and operate the contactor 34. When cores l5 and [6 make contact a short circuit will be provided across the power source 35 and potential will be removed from machine 40. The short circuit provided by device 34 includes safety device 38 wihich will be operated by the large current flowing therethrough to open the circuit.

The small diameter of the coil 25 in the short circuiting contactor, described above, is conducive to high speed operation as the accelerating force on cores iii and I5 is dependent upon the product of the amperes and the turns in coil 25. The speed of closing of the gap is inversely proportional to the inductance of the operating coil. Since the inductance of the operating coil is affected by its diameter, the small diameter permitted by this construction causes the contactor to operate at very high peed. A fiat strip winding permits still further reduction in the physical diameter of the device.

The simplicity of the design makes this device particularly adaptable for cable tap service in mechanized coal mines and tends to reduce the manufacturing cost. The light weight of such a contactor, compared with the air break circuit breaker for equivalent service, would be advantageous in any portable device with, trailing cables. Practice has shown a virtual absence of arcing and burning in relation to the magnitude of current handled, an advantage thought to be attributable to the position of the contacts in the magnetic field of the winding 25. V

The embodiment and applications of this invention described above are exemplary only and many modifications and additional adaptations will occur to those skilled in the art within the scope of the appended claims.

What is claimed is:

1. In an electrical distribution system for use in mines, a utilizing device and a pair of transmission wires carrying direct current, one wire having a relatively low potential and the other wire having a relatively high potential, said utilizing device being connected across said low and high potential wires, there being a safety device between said high potential wire and said utilizing device, said utilizing device having a metal frame, a contactor device comprising a coil connected between. said low potential wire and said frame, and a pair of axially movable cores within said coil normally separated but arranged for rapid closing when the current in said coil exceeds a predetermined value, one of said cores being connected to said low potential wire and the other of said cores being connected to said high potential wire through said safety device, said safety device being located remotely from said utilizing device and arranged to open when the current through said safety device exceeds a predetermined value.

2. The combination of claim 1, in which the utilizing device and the contactor device are located in an enclosure subject to being filled by an explosive atmosphere and in which said safety device is located in a position where it is not subject to enveloprnent by an explosive atmosphere.

LAWRENCE H. HARRISON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,017,198 Bender Feb. 13, 1912 1,024,251 Fielding, Jr Apr. 23, 1912 (Other references on following page) Number 5 UNITED STATES PATENTS Name Date Simon June 15, 1915 Smith Jan. 12, 1926 Benson Oct. 12, 1926 Tinsley et a1. Oct. 12, 1923 Benson Dec. 20, 1927 Gillen Oct. 3, 1933 Leece et a1 May 14, 1935 Sharp May 11, 1937 Schmitt Apr. 19, 1938 Gardiner Aug. 22, 1939 Number Name Date Weichsel May 26, 1942 Matthews Nov. 16, 1943 Dries June 24, 1943 FOREIGN PATENTS Country Date Germany Sept. 10, 1919 Great Britain Jan. 29, 1934 Germany Mar. 3, 1935 Great Britain July 20, 1937 Great Britain Nov. 15, 1937 

